cherif kouachi was arrested as he was about to board a plane to go to iraq and fight. >> narrator: kouachi was sent to fleury-mérogis prison to await trial. while he was locked up, his extremist connections only deepened. the prison was a hotbed of jihadism dominated by al qaeda veterans. kouachi became friends with another radicalized criminal who would ultimately join him in his terrorist project: amedy coulibaly. >> (translated): they could communicate with each other. it was totally porous. it was disturbingly easy to form connections. so they expanded their network and became worse than when they >> narrator: marc trévidic was a top counterterror prosecutor and judge who investigated kouachi's network. he says the french judicial system was not set up to deal with the long-term threat they posed. >> (translated): that was our tragedy, in a way. we thought that if there are no attacks on french soil, then the anti-terrorist system is working correctly, therefore everything is fine. in fact, nothing was fine. these may have been terrorists linked to al qaeda, but they were seen as peopl